"Reload an ES module and its dependencies"
npm install esm-reloadThis module lets you reload an ES module and its dependencies in Node.js. It does so by adding a module resolution hook.
Per spec, ES modules are cached the first time they are imported, and subsequent import statements return the same object.
``JS
import {assert} from 'node:assert/strict'
const m1 = await import('./my-module.js')
const m2 = await import('./my-module.js')
assert.equal(m1, m2) // passes
`
This is desirable in most scenarios, but you can sometimes want to instantiate a module several times. For example, you may want to test a module that branches at load time depending on its environment. To some extent, that can be achieved by tacking a query string at the end of the import specifier:
`JS
import {assert} from 'node:assert/strict'
const m1 = await import('./my-module.js?dev')
process.env.NODE_ENV='production'
const m2 = await import('./my-module.js?prod')
assert.notEqual(mDev, mProd) // passes
`
However, this doesn't work transitively. ./my-module.js?prod will import the dependencies that were cached when ./my-module.js?dev was loaded.
If you want to load a module multpile times from scratch with its dependencies you can use this module.
The resolver hook gives a special meaning to ?instance=... and ?reload query strings.
If you want to retrieve a specific instance, use the former with an identifier of your choice.
`JS
import "esm-reload" // this registers the hook
const mDev = await import("./myModule.js?instance=dev")
process.env.NODE_ENV='production'
const mProd = await import("./myModule.js?instance=prod")
const mDev2 = await import("./myModule.js?instance=dev")
assert.equal(mDev, mDev2) // passes
assert.notEqual(mDev, mProd) // passes
`
If you just want a fresh instance you can use ?reload
`JS
const mReloaded = await import("./myModule.js?reload")
assert.notEqual(mDev, mReloaded) // passes
assert.notEqual(mProd, mReloaded) // passes
// ?reload is "magic"
const mReloaded2 = await import("./myModule.js?reload")
assert.notEqual(mReloaded, mReloaded2) // passes
`
In both cases, instances come with a fresh set of dependencies (except for the builtin node:xxx modules that don't support query strings at all).
Suppose these files:
`JS
// foo.js
export {x} from "./bar.js"
// bar.js
export const x = {}
`
We can then do
`JS
import "esm-reload"
const foo1 = await import("./foo.js?instance=1")
const bar1 = await import("./bar.js?instance=1")
const foo2 = await import("./foo.js?instance=2")
const bar2 = await import("./bar.js?instance=2")
assert.equal(foo1.x, bar1.x)
assert.equal(foo2.x, bar1.x)
assert.notEqual(bar1.x, bar2.x)
``
The hook was originally written by Marcel Laverdet(@laverdet) then tweaked, tested and documented by yours truly.
ISC